The aim of the study was to evaluate whether the imbalance between IL-12 and IL-13 serum levels, reflecting Th1/Th2 activity, is related to class-specific circulating rheumatoid factors (RF) and anticardiolipin (aCL) antibodies in SLE. Using ELISA we measured serum IL-12, IL-13, RF and aCL antibodies in 73 SLE patients and 20 healthy controls. The determination of IL-12/IL-13 ratio showed that IL-12 levels were above (group A), equal to (group B) or below (group C) IL-13 levels in 71.2%, 15.1% and 13.7% of SLE patients, respectively. IgM-RF levels were significantly higher in group C than in groups A ( P < 0.002) and B ( P < 0.019). Group C had also higher IgM-aCL levels than group A ( P < 0.04). No relationship between IL-12/IL-13 ratio and clinical or other laboratory parameters was found. It was concluded that the increased levels of both IgM-RF and IgM-aCL in patients with prevalent Th2 activity suggest that the predominance of Th2 over Th1 could drive autoantibody production in SLE patients.